Lithium-Assisted Electrochemical Welding in Silicon Nanowire Battery Electrodes

Abstract

From in situ transmission electron microscopy (TEM) observations, we present direct evidence of lithiumassisted welding between physically contacted silicon nanowires (SiNWs) induced by electrochemical lithiation and delithiation. This electrochemical weld between two SiNWs demonstrates facile transport of lithium ions and electrons across the interface. From our in situ observations, we estimate the shear strength of the welded region after delithiation to be approximately 200 MPa, indicating that a strong bond is formed at the junction of two SiNWs. This welding phenomenon could help address the issue of capacity fade in nanostructured silicon battery electrodes, which is typically caused by fracture and detachment of active materials from the current collector. The process could provide for more robust battery performance either through self-healing of fractured components that remain in contact or through the formation of a multiconnected network architecture.

Chemomechanical modeling of lithiation-induced failure in high-volume-change electrode materials for lithium ion batteries

“…Surface coatings can also prevent electrochemical welding between particles of active materials. 128,129 In uncoated Si, lithiation generated compressive stress at the reaction front and in the a-Li x Si phase, slows down the reaction and Li diffusion, causing lithiation retardation. In the presence of surface coating, the constraint of the coating may cause even high compressive stress inside the SiNP as the SiNP swells, 112,116 which modifies the driving force both for chemical reaction at the reaction front and the diffusion behind, as shown in a comparative study for pure Si and Si coated with elastic coating in Fig.…”

Review—Promises and Challenges of In Situ Transmission Electron Microscopy Electrochemical Techniques in the Studies of Lithium Ion Batteries

“…35,36 Thirdly, fracture of the active electrode material uncovers more surfaces to the electrolyte, resulting in spontaneous formation of additional SEI layers which accelerate the loss of capacity-though they also act as a protective film against electrolyte decomposition at the electrode-electrolyte interface. 12,18 One method to overcome detrimental effect like the huge volume changes that occur in the new high-capacity electrode materials is the use of nanoscale or nanostructured materials, such as nanorods, 37,38 nanowires, [39][40][41] and nanotubes [42][43][44] to substitute for the micrometersized materials that were used in the first generation of LIBs. A good example of the use of nanoscale electroactive materials is the Ge-nanoparticle (NP) anode that retains high capacity without any noticeable cracking through ∼260% volume changes after multiple cycles.…”

“…24,25,41,130,149 Moreover, Si NWs in physical contact can weld together at their junctions by generating strong interfacial bonding after lithiation and delithiation. 41 The fusion at the Si NWs interfaces provides facile Li diffusion between surfacecontacted NWs, and may enable the self-assembly and self-healing of an interconnected network of Si NWs, because the detached NWs can still participate in Li storage after they form a robust interconnected network.…”

“…41 The fusion at the Si NWs interfaces provides facile Li diffusion between surfacecontacted NWs, and may enable the self-assembly and self-healing of an interconnected network of Si NWs, because the detached NWs can still participate in Li storage after they form a robust interconnected network. 41 However, a highly unexpected anisotropic expansion or fracture strain of crystalline silicon (Si) NWs or a strong size-dependent fracture for Si NPs (because of the competition between the stored mechanical energy and the crack propagation energy of the NPs) were recorded during lithiation, resulting in a necking instability and fracture. 74,130,[150][151][152][153][154] The fracture energy of the lithiated Si was essentially independent of the lithium concentration; it was not notably changed with the variation of lithium concentration, and was very close to the value of pure Si.…”

Phase Equilibria and Phase Separation of the Aqueous Solution System Containing Lithium Ions

“…Lithium is the lightest alkali metal, which plays a growing role in numerous processes such as rechargeable batteries, thermonuclear fusion, medical drugs, lubricant greases, ceramic, glasses, dyes, adhesives, and electrode welding [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Lithium is a critical energy material and a strategic resource for the twenty-first century.…”